Tuesday, February 20, 2018

Conquering RFI in the 2C22/7193


Noisy and unstable 2C22/7193

Moving closer to civilization, this lovely sounding triode used as a voltage gain stage in my SE2A3 mono integrated amp had stability issues due to RFI. 



Since I persist in using these antediluvian devices, I had to find a solution.


A 150 ohm 1/2W CC resistor with the leads cut short soldered in series with the grid cap (insulate with heat shrink tubing) >> shielded cable terminated by an RCA plug (shield connected only at the RCA jack side) >> RCA jack (barrel grounded to chassis) solved the stability issue.

A well behaved 2C22/7193 

2 comments:

  1. Are you using shielded cable to the grid? When using very high transconductance tubes like the 5842/417 or 437 grid stoppers are pretty much mandatory, 417/5842 has 4 grid pins, have to use one on each pin....

    Roscoe

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    Replies
    1. Yes, shielded cable was good enough before. Now the grid resistor was the only cure. Maybe it's my proximity to more airwaves?

      JE

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